Carbon resistance



May 13, 1930. H. GROB CARBON RESISTANCE Filed Jan. 2'7. 1927 Patented May 13, 1930 PAT ENT OFFICE HUGO G303, OF BERLIN, GERMANY CARBON RESISTANCE application fled January 27, 1927, Serial No.

This invention relates to resistances comnosed of discs of carbon. v

In regulating the voltage of electric h hting sets for railwa vehicles it is usua 1n 5 many cases to emp oy a varlableresistance composed of a column of carbon discs, whlch is switched in front of the net-work, and which cuts down the voltage to such degree that the correct number of volts remain for the lamps. This colunm is made to assume different degrees of resistance by means of varying pressure, and the same is required to devour the excess generator voltage (which depends upon the accumulator charging voltage) beyond the nominal voltage of the lamps.

In this manner the column of carbon discs is frequently required to convert quite considerable amounts of energy into heat, and

in such cases it is necessary to artificially increase the surface area in order to avoid excess temperature.

It has hitherto been usual, in the case of given dimensions of the disc area, to erform this increase b making the discs thlcker than is absolutel necessary for the required strength. bus, with equal resistance and loss of watts, the column was 1ncreased in length with corresponding increase in the cooling area. In practice the resistance of the column is determined only by the number of and the pressure applied to the contacting faces of the discs, and not by the distance which the current is required to traverse in the carbon.

A difficulty arising in connection with resistances of this type resides in the disturbing effect occasioned by the expansion of the column under heat.

In passing over from the lowest to the greatest pressure on the column, the latter varies in length by a certain amount. Within this compression distance the reaction force of the column naturally varies to a 4 considerable degree, and assumes an extremely high value when the discs are pressed very closely together.

With every length of column the reaction force within the compression distance must a l be made to balance with two other forces,

164,115, and in Germany February 10, 1926.

viz., the force of a spring, which tends to compress the column, and with the pull of a magnet, which is excited by the voltage to be regulated, and which again relieves the column to a certain extent.

Towards the end of the stroke where the discs are pressed together, every one-tenth millimetre additional compression causes a very rapid increase in the reaction force.

In accordance with exactly the same law, the pressure exerted by the mechanism on the column must also increase with this displacement if a state of equilibrium between the three forces referred to is to exist in every position of the mechanism.

If, on account of excessive heating; the column is somewhat extended in lengt the as in connection with the shorter length in cold state, but the pressure applied by the mechanism has been varied by the displacement, a disturbance has been caused in the state of equilibrium which requires to be again readjusted by variation in the magnetic force, i. e., by variation in the exciting voltage. This is equivalent to a corresponding error in the voltage regulation. It is obvious that this error will be all the greater the thicker the carbon discs, i. e., the longer the column with the same number of discs and accordingly the more the same expands under heat.

The present invention covers a method of arranging resistances composed of carbon discs, in which with equal surface area of the column the error in the voltage regulation caused by expansion under heat is considerably less than in the case of the hitherto known arrangements.

The essence of the invention consists in producing in the case of a carbon column with given cross-sectional exterior dimensions the -desired increase in the surface area, not by making the discs thicker, but by adding to the original column one or more additional columns with discs of like thickness and switching'the same in parallel with the original column.

' example, are annular in form, the halving of the cross-section may be performed for instance by increasing the inner diameter, or in the case of imperforate discs by providing incisions or scallops, or by varying the crosssectional form, it being qu1te understood, of

course, that the cooling area should at least not be diminished.

By halving the cross-section of the column it is necessary, for attaining a like specific pressure, to halve the total pressure applied. Thus the mechanism is also required to exert merely half the pressure, and consequently the disturbing effect of the expansion of the column on the compensation of the forces will also behalved.

In reality, however, the error is reduced to less than the half. If the compression disstance of a column composed of twice the number of discs of half the thickness were also twice as great as the compression distance of a column composed of half the number of discs of twice the thickness, the transmission stroke of the mechanism on the carbon column in the case of the thin discs would be twice as great as in the case of the thick discs, and the amount of work required to be performed by the mechanism (half the force times the doubled distance) would remain the same. In this case the disturbing influence of the heat would be exactly half that in the case of the thick discs, since the expansion distance of the column in comparison with the compression distance is now only half as great.

However, the compression distance of a column composed of a greater number of thinner discs is by no means greater in proportion to the number of discs than that of a column of equal length having thicker discs, so that on account of the favorable transmission of the mechanism the reaction of a variation in the reaction force on the equilibrium of the magnet is again reduced.

In the drawing Fig. 1 shows a form of embodiment of the invention;

Figs. 2 and 3 showing an additional detail.

In Fig. 1 the carbon discs of the column are designated A, and are, for example, of annular form. B represents three metal rings sup lying current, of which the one is situate in the centre and the other two each at the two ends of the column. C and D are the leads through which the current is supplied, and are so attached that the upper and the lower halves of the column are connected in parallel.

In lieu of the columns switched in arallel being placed axially to each other, t e same might also be arranged side by side. This arrangement, however, causes complications in the transmission mechanism, and also requires an unnecessary amount of space. Moreover, inexactitudes are noticeable in the mechanism-if the movements occur over a small distance and the force is relatively strong.

Certain advantages are offered by vertical disposal of the resistance column. This position, however, means that the lower sections of the column are required to bear the weight of those above, and are consequently never entirely relieved, and they do not increase their resistance when the column is fully relieved to the same-extent as the topmost section.

The invention also relates to a device which overcomes this drawback. The same consists in counterbalancing in the case of each section of the column, with exception of the lowest one, the pressure on the base by means of small counterweights. The appertaining Figs. 2 and 3, forming elevation and plan, show a form of embodiment given by way of example. As in Fig. 1, A designates the discs of carbon, and B metal rings supplying the current. As opposed to Fig. 1, however, two metal rings are provided at the centre of the column, of which the upper one possesses three outwardly projecting lugs E. Each of these is sup orted by the end- F of a twoarmed'lever (E, which is furnished at the other end with a small weight H. The lever G is supported at the centre by a knife-edge J.

The weights H are of such weight as to practically entirely counterbalance the pressure between the two metal rings in the centre. In order upon jolts to prevent a break in the current by the two sections of the column opening apart, the lower ring is inserted between, which is electrically connected with the upper ring, and on account of its weight always remains resting on the lower section of the column.

Due to the weights H the lower half of the column, when the load is entirely removed from the same, is also fully relieved.

In view of the foregoing, it will be clear that any suitable means may be employed to constitute a transmission mechanism for applying to the column of carbon disks the intended pressure to suit the conditions of practical use and merely by way of illustration of a possible form of mechanism for applying pressure to the carbon pile and relieving the latter from pressure, I have shown in Figure 2 diagrammatically a lever 11 pivoted as at 10 the upper end of the column and (provided with a suitable member 12 secure thereto as at 13, for enga ement with of carbon spring 14'may serve to swing the disks. A

lever 10 about its pivot 11 so as to cause the carbon pile to be compressed, and a magnet or solenoid 15 may act in opposition to the spring 14 and is adapted'to respond to the electrical conditions in the circuit to be regulated and thus to control the transmission of force or pressure to the carbon pile.

It will thus be seen that there has been provided in this invention a carbon resistance in which the several objects hereinbefore noted,

as well as many thoroughly practical advantages, are successfully achieved. It will also be noted that the apparatus is'well adapted to meet the varying conditions of practical use.

As man possible embodiments may be made of tlie above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as illustrative and not in a limiting sense.

What I claim as new and desire to secure by Letters Patent is:

1. In apparatus of the character described, in combination, a carbon pile extending substantially vertically, means for varying the pressure on said pile thereby to va its resistance, a counter-Weight of substantially the same Weight as that of an upper section of said pile, and means connecting said counterweight to the lower portion of said upper section of said pile to substantially balance the weight of said upper portion.

2. In apparatus of the character described, in combination, a carbon pile extending substantially vertically, means for varying the pressure on said pile thereby to varyits resistance, means for sectionalizing said pile comprising conductive members, one at the bottom of each section and one at the top of each section, means for connecting said sections in parallel and comprising conductors connected to said conductive members, and means acting through the conductive mem her at the bottom of one section and exerting an upward force sufiicient to prevent the weight of said one section from substantially affecting the resistance of a section underneath said one section, the members of said pile being apertured and said conductive members being substantially of plate-like form and apertured, all of said apertured, members being related so that the apertures therein are in inter-communication to form an open-ended passage.

In testimony whereof I have signature.

HUGO GROB. 

